Assuming that Dragon Isles is the focus on the next expansion, I would guess it would be similar to Broken Isles in Legion, with different sections being different zones.
If it isn’t the focus, it could be something on a smaller scale like with Mechagon and Nazjatar, though I feel like that would be a bit too small for such an area. Maybe it would be something a bit bigger but the focus of a major patch. If this is the case, I’m not sure what the next expansion’s theme would be at all.
A thing about that “leak” was a mention of how some of the older zones would get a big update of some kind. I’m wondering that if Dragon Isles is the focus of the next expansion, if Dustwallow Marsh could see such an update. Onyxia’s lair was there, and who knows what has happened to it since we killed her. Maybe something of importance is still there or some evil dragons, maybe of Onyxia’s brood, could come back to take it over for something insidious.
If so, we could at least see an in-game update on the MU Stonemaul Clan there, given they’re a big part of that zone (in several ways). Honestly, if we deal with evil dragons, especially if there are any evil Black Dragonflight members, it would be a good time to introduce that and give the MU Stonemaul Clan some revenge.
Of course, I won’t get my hopes up. This is all just speculation, with a dash of hope of course. I do hope whatever the next expansion is, we get an official announcement soon. I can wait for it to be developed and hopefully it won’t get rushed. I just want to see the direction the game’s story is going and what features are coming with the next expansion.
Dream big, Ogre fans! 
